Simple amine compounds are known to provide neutralizing, dispersant and hardening properties when added to coatings, mineral slurries and epoxy formulations. Methods for simple amine compound manufacture are well-documented and known in the art, and when the goal is to prepare primary amines, the preferred routes often involve intermediate nitro alcohol compounds.
Processes for the manufacture of the intermediate nitro alcohol compounds, are known and typically nitro aldol reaction (Henry Reaction) between nitroalkanes and aldehydes. There has been occasional reference to the preparation of dinitroalcohols involving a tandem Michael addition and Henry reaction of a nitroalkane with an α,β-unsaturated aldehyde. For example, see “Secondary dinitro alcohols,” Smith, Curtis W. (Shell Development Co.) 1949, and U.S. Pat. No. 2,475,996, which describe the manufacture of the nitro alcohol 2,5,6-trimethyl-2,6-dinitro-3-heptanol. This nitro alcohol is also prepared as an intermediate to making a vasopeptidase inhibitor, as discussed in Efficient Asymmetric Synthesis of the Vasopeptidase Inhibitor BMS-189921 by Janak Singh et al., Org. Lett. (2003), 5, 17, 3155-3158. In addition, manufacture of the nitro alcohol compound 2,6-dinitro-5-phenyl-heptan-3-ol has been described in David St. Clair Black et. al. Australian Journal of Chemistry, 1976, 29(11), 2511. As is also well-established, nitroalcohol compounds may be readily converted to the amino alcohol compounds by hydrogenation with hydrogen over a suitable catalyst, for example Raney nickel or a platinum- or palladium-based catalyst (Pt or Pd in elemental form or as oxides, with or without supports, e.g., carbon). Those skilled in the art are also aware that other reducing agents which will reduce nitroalkanes to primary amines include metal/acid combinations, e.g., iron/acetic acid; and aluminum hydrides. The preferred reducing agents include hydrogen gas in combination with any of the following catalysts: Raney nickel, platinum or palladium.
Diamino alcohol compounds and their uses, on the other hand, are not currently represented in the prior art.
Amines and amino alcohols are known to be hardeners, or curing agents, for epoxy resins. There are a number of amines that are currently used commercially as hardeners or curing agents that result in resins with high Tg, however, these are typically cycloaliphatic or aromatic diamines. Some of the examples of amines and the Tg of the resin produced when cured with D.E.R. 331 epoxy resin commercially available from Dow Chemical Company, Midland, Mich., include cyclohexane-1,2-diamine (Tg: 152° C.); isophorone diamine (IPDA) (147° C.) and 4-((4-aminocyclohexyl)methyl)cyclohexanamine (163° C.). Diamines that are straight chain aliphatic are useful as hardeners, but typically do not result in a resin with high Tg. Examples of aliphatic diamines are Dytek (Tg: 104° C.), AEP (Tg: 106° C.) and TMD (Tg: 104° C.). Similarly, amino alcohols are used as hardeners or curing agents commercially today, due to their ability to cure at lower temperatures than simple amines, but these amines also do not enable the formation of cured epoxy resins with high glass transition temperatures (Tg). Some of the most common examples of amino alcohols include, without limitation, ethanolamine (EA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP) which is commercially available from ANGUS Chemical of Buffalo Grove, Ill., USA), and 2-amino-2-ethyl-1,3-propanediol (AEPD) [Asghar checking whether we have Tg data for any of these amino-alcohols], also commercially available from ANGUS Chemical of Buffalo Grove, Ill., USA, etc. Well-known and heavily used amine hardener systems in the industry include, but are not limited to, isophoronediamine (IPDA), meta-xylenediamine (MXDA), aminoethylpiperazine (AEP), ethylenediamine, etc. Additionally, the use of TRIS-AMINO, which is a non-volatile alkanolamine possessing primary amine functionality commercially available from ANGUS Chemical of Buffalo Grove, Ill., USA, has been reported in the patent literature. U.S. Pat. Nos. 4,330,644, 3,607,833 and 7,001,938, as well as U.S. Patent Application Publication No. US2007/0065669, each describes the use of TRIS-AMINO in various epoxy-based compositions.
However, many of the amino alcohol-based hardeners currently used only provide cured epoxy resins with glass transition temperatures of less than about 120° C. and are, therefore, often unsuitable for high temperature applications. An amino alcohol based hardener that can result in a resin with a high glass transition temperature (i.e., greater than about 120° C.) useful for high temperature applications would be of value. The added advantage of amino alcohol versus simple aliphatic amines is the improved properties resulting from the presence of the alcohol functionality. There is literature precedent that the adhesion performance of an epoxy coating is due to the interaction of hydroxyl groups with the surface to which the coating is applied. Furthermore, It is also known, that hydroxyl group has catalytic effect in the curing profile, thus enabling cure at lower temperatures (see, for example, U.S. Pat. No. 3,943,104).